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IACSIT International Journal of Engineering and Technology, Vol.2, No.6, December 2010
ISSN: 1793-8236
An Advanced Architecture & Instrumentation
for Developing the System of Monitoring a
Vital Sign (Oxygen Saturation) of a Patient.
1
Md.Mokarrom Hossain, 2A.S.M.Mohsin*, 3Md.Nasimul Islam Maruf, 4Md. Asaduzzaman Shoeb*
and 5Ifat Al-Baqee
Abstract—Bio-Medical Engineering (BME) has been an
active research area for years. BME is the application of
engineering techniques to the medical fields. It combines the
design and problem solving skills of engineering with
medical sciences to improve the health care and the quality
of individual life. With the proliferation of advanced
electronics and applied engineering, the ways to help people
specifically patients are changed. Therefore, an advanced
design for monitoring a vital sign towards experimentation is
presented. The vital signs monitor is essentially a real time
device that displays certain received signals from the human
body. The projects of this sort under taken so far have used
windows to display the output whereas this project aims to
generate a real time display of the signals received from the
human body using Linux. Linux was preferred for its ability
to simultaneously process data and display it in real time.
The basic principles and methods are outlined. The major
components of the system are shown separately, and are
discussed individually. Few electronic devices used for data
are depicted and described. The final results show a better
performance
Index Terms—Oximeter, Data Acquisition Card, Pulse
Oximetry, Design Process Overview, Result Analysis
I. INTRODUCTION
The objective of Patient Monitoring Systems is to have
a quantitative assessment of the important physiological
variable of patients during critical periods of biological
functions. For diagnostic and research purposes it is
necessary to know actual value or trend of change of this
variable. Patient monitoring systems are used for
measuring continuously or at regular intervals,
automatically, the values of patient's important
physiological parameters.
There are several categories of patients who may need
continuous monitoring or intensive care. Critically ill
patients recovering from surgery, heart attack or serious
Manuscript Received September 29, 2010.
1
Md.Mokarrom Hossain, 2A.S.M.Mohsin, 3Md. Nasimul Islam
Maruf ,4Md. Asaduzzaman Shoeb, 5 Ifat Al-Baqee, is with(1-5),
Department of
Electrical and Electronic Engineering, Stamford
University Bangladesh,51Siddeswari, Dhaka1217,Bangladesh..
*
Member
of
IACSIT
(email:[email protected],[email protected],3mrf5
[email protected],[email protected], [email protected])
illness, are often placed in special units, generally known As
intensive care units, where they can be supervised constantly
by the use of electronic instruments. The main features of
patient monitoring systems:
• Organizing and displaying information in a meaningful
form to improve patient care.
• Correlating multiple parameters for clear demonstration of
clinical problems.
• Processing the data to set alarms on the development of
abnormal conditions.
• Ensuring better care.
The most often monitored biological functions are
Electrocardiogram (ECG), heart rate, pulse rate, temperature
and respiratory rate. Among this oxygen saturation is the
centre of this thesis.
II. PULSE OXIMETER, OXYGEN SATURATION (SPO2)
Oximeter is based on the concept that arterial oxygen
saturation determinations can be made using two wavelengths.
The two wavelengths assume that only two absorbers are
present, ox hemoglobin and reduced hemoglobin. Light
passing through the finger will be absorbed by skin pigments,
tissue, cartilage, bone, arterial blood, venous blood but this
absorption is indifferent to the wavelength of the light being
passed through it. Therefore the absorbance by all these helps
us in the determination of oxygen saturation in the blood.
III. DATA ACQUISITION CARD
The Data Acquisition Card (DAQ card) was used to digitize
the analog output of the circuits. Certain changes were made to
the circuits to accommodate this process. The DAQ card fed
its digitized data to the computer which worked using Linux.
This ensured real time display as the aim of this project was to
enhance the real time display characteristics of a Vital Signs
Monitor.
A. Medical background
Pulse oximetry is a non-invasive and continuous method of
determining the amount of oxygenated and deoxygenated
hemoglobin in a person’s blood supply. It is preferable to have
a direct measure of the oxygen levels in hemoglobin because it
can be determined in real time while causing no discomfort to
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IACSIT International Journal of Engineering and Technology, Vol.2, No.6, December 2010
ISSN: 1793-8236
the patient. Traditional pulse oximeters
measurements from the finger and ear lobe.
take
B. Mathematical Aspect
Pulse oximetry is accomplished by implementing the
Beer-Lambert Law, which, in this case, relates the
concentration of oxygen in the blood to the amount of
light absorbed when transmitted through the blood. The
absorption of the light transmitted through the medium
can be calculated using the Beer-Lambert Law as follows:
IOUT = IIN e-A ……………… (1)
Where IOUT is the intensity of the light transmitted through
the medium, IIN is the intensity of the light going into the
medium, and A is the absorption factor.
Fig1: The absorption coefficient for the two types of hemoglobin as a function
of wavelength.
Pulse oximetry uses two light emitting diodes (LEDs) or
light sources of similar kind with known wavelengths, one
LED emitting red light and the other infrared.
C. A brief history of oximetry
To be able to design a pulse oximeter the theory
behind how the body absorbs oxygen and how the
absorption of light works must be clear. The knowledge
that is used is that saturated hemoglobin is light red and
non-saturated hemoglobin is dark red.
The first pulse ox meter was designed in the late 1930’s
by German researchers whose objective was to measure
the oxygenation of “high altitude pilots.”[6] From that
point on, the pulse ox meter, as it was later called, has
been improved upon continuously.
The first pulse oximetry was invented in 1972 and has
grown to become an increasingly important technique in
Intensive Care Units and medical care in general. It is a
simple non-invasive method of monitoring the percentage
of hemoglobin (Hb), which is saturated with oxygen.
There are two methods of sending light through the
measuring site:
• Transmission and
• Reflectance.
In the transmission method, a photo detector detects the
light that passes through.
In the reflectance method, it is also possible to have the
photo detector placed right next to the LEDs and have it
receiving the reflected light.
This method is not as common. The transmission method is
the most common type used and for this discussion the
transmission method will be implied.
D. Principles of Pulse Oximetry
The purpose of a pulse oximeter is to measure the
percentage of hemoglobin, which is saturated with oxygen.
The theory behind the technique is based on the red and
infrared (IR) light absorption characteristics of
oxygenated and deoxygenated hemoglobin. Oxygenated
hemoglobin absorbs more infrared light and allows more
red lights to pass through. For deoxygenated hemoglobin
it is the other way around. Deoxygenated hemoglobin
absorbs more red lights and allows more infrared light to
pass through. Red light is in the 600-750 nm wavelength
light band. Infrared light is in the 850-1000 nm
wavelength light band. Figure1 shows the absorption
coefficient for both types of hemoglobin at different
wavelengths.
Fig 2: Basic idea of a pulse oximeter of haemoglobin at red and infrared
wavelength.
Two signals will be generated by the photodetector, one
signal created by the red light, and another signal created by
the IR light. The signals will differ from one another because
of the difference in light-absorption discussed above. The
more oxygen there is in the blood, the more the two signals
will differ. Obviously, the tissue will absorb light as well, but
since the tissues’ absorption coefficient is identical for both
wavelengths, it will not affect the result.
Absorption on each wavelength differs significantly for the
oxyhaemoglobin and deoxygenated haemoglobin. Therefore
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IACSIT International Journal of Engineering and Technology, Vol.2, No.6, December 2010
ISSN: 1793-8236
from the difference of the absorption of the red and
infrared light the ratio between oxy/deoxyhaemoglobin
can be calculated. As the amount of blood in the
capillaries depends on the actual blood pressure, which
varies around the heart, the heart pulse cycle and in turn
the heart rate can also be measured.
Oxy hemoglobin refers to oxygen carrying
haemoglobin and deoxygenated haemoglobin refers to
non oxygen carrying haemoglobin. If all haemoglobin
molecules bonded with an oxygen molecule (O2), the total
body of haemoglobin is said to be fully saturated (100%
saturation). When haemoglobin unloads the oxygen
molecule to tissue cells at capillary levels, the saturation
progressively decreases and the normal venous saturation
is about 75%. The normal saturation level is said to be
between 87-97%.
The two wavelengths are chosen because deoxygenated
haemoglobin has a higher absorption at around 660nm
and at 910 nm oxygenated hemoglobin has the higher
absorption.
The measurement Process: The measurements taken
by the pulse oximeter demonstrate the shape of a pulsatile
waveform as seen in fig3. This pulsatile waveform has
both AC and DC components in it. The DC components
are comprised of the absorption from the non-pulsing
arterial blood, the venous and capillary blood, as well as
from scattering and absorption due to the tissue and bone.
These components are always constant and rest on one
another as shown in the figure. The AC component of the
figure 4 is the pulsatile waveform that we are interested in.
Fig 5: AC and DC components of oximetry
This waveform represents the pulsing of the blood in the
arteries and each individual pulse can be seen, representative
of the heart rate. This waveform is gathered for both light
frequencies, in this case infrared and red light. In order to
obtain the pulse oximeter saturation (Sp02), these AC and DC
components from each of the wavelengths need to be
measured and taken as a ratio as follows:
R =[ACλ1/ DCλ1]/[ ACλ2/ DCλ2]
Ratio,
R =
(AC
(AC
DC
DC
)
)
(2)
r
i
SPO2= (110 – 25R)%
E. Calibration
This ratio is then used in a calibration curve based on
studies of healthy individuals to determine the Sp02. This
value will end up being a percentage which will tell the
physician whether or not everything is as it is supposed to be.
A normal saturation level is between 87-97%. This method of
measuring the Sp02 has been shown to be accurate to within
2.5%.
F. Oxygen Saturation Circuit requirements
Fig 6: General Pulse Oximeter Circuit Diagram
Fig 3: AC and DC components of oximetry
Fig4: AC and DC components of oximetry
The sensor is to be made out of a black rubber-made tube. It
is important to use a material that does not reflect so much
light and does not let light through the surface. The front of the
tube was tightened with a black plug to avoid surrounding
light will affect the result. Two holes are drilled in the top part
of the tube, for the two diodes (660 nm and 940 nm) and two
holes in the bottom part for the Photodiode. The electronics
are set up on a lab-board. It's built by connecting the
Photodiode of the sensor to an amplification circuit.
The following instruments have been used to power the
electronics and to measure the result:
• 1 multimeter Fluke 45 dual display multimeter
• 1 oscilloscope HAMEG 60 MHz HM604
• 1 power supply D2510.
G. Design Process Overview
Due to the dearth of sensors in the market, it was required to
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IACSIT International Journal of Engineering and Technology, Vol.2, No.6, December 2010
ISSN: 1793-8236
attempt reverse engineering to construct a signal that will
be similar to that expected to be received by the circuit.
Under this objective, the circuits required can be broken
down into certain parts.
environmentally induced noise.
Fig 7: Flow Chart
H. Complete Probe and Circuitry Prototype
Construction
The pulse oximeter design consists of LED excitatory
circuits as well as photodiode sensory circuits; the
receiving circuits convert the red and infrared light
currents into voltages which can then be observed using
an oscilloscope. Signal voltage data is then recorded and
post-processed in excel in order to obtain blood oxygen
saturation levels. The approach can be broken down as
follows:
1) Two light emitting diodes (LEDs), of red (600 to
750 nm) and infrared (940 nm) wavelengths
were directed at tissue and activated by an
excitatory circuit.
Fig 8 and Fig 9: Trans impedance Amplification Circuit
The above two circuits were implemented. Red and Infrared emitters and detectors were implemented into separate
circuits
IV. EXPERIMENTAL DATA OF OXYGEN SATURATION
Thickness
1
2
3
4
5
6
7
8
9
10
2) The light emitted from the LEDs were
transmitted through the skin and detected by two
photodiodes. An infrared rejection filter
photodiode was then placed across from the red
LED in order to detect transmitted red light and
prevent infrared light interference. Similarly, a
visible light rejection filter photodiode was
placed across from the infrared LED with similar
intentions.
3) The two photodiodes were then connected to a
trans impedance amplification circuit that
converted the current to an appropriatelyenhanced voltage signal.
I. Amplification
The pulsating changes in transmitted light through the
patient are very weak, and so the analog signal output of
the frequency to voltage stage is also very small in
amplitude. Therefore, a high gain amplifier stage is
required to provide a suitable waveform. The high gain of
the circuit requires that it also be immune to
601
Output(v)
0.517
0.515
0.51
0.509
0.508
0.507
0.506
0.506
0.505
0.505
IACSIT International Journal of Engineering and Technology, Vol.2, No.6, December 2010
ISSN: 1793-8236
Fig 10: Thickness vs. Output Voltage
A. Result Analysis
Unfortunately, the devices available in the market here
are not appropriate for the circuit. Hence proper output
was never recorded in this channel. However, we
conducted reading based on paper thickness and tabulated
it. A positive correlation was observed in this data
analysis.
V. CONCLUSION
In this project we tried to ameliorate the overall
performance of a oxygen saturation monitoring system.
The entire architecture is implemented which successfully
reads output through the DAQ card and displays it in soft
real time. The purpose of the project was to enhance the
real time properties of the display of human physiological
variables and that has been successfully implemented and
recorded.
To extend its application, it will be possible to use the
same channel and feed the input into the DAQ card which
in turn will provide the digitized input to the Linux
computer. Real time Linux can be used in this project
without any further modification the input into the DAQ
card which in turn will provide the digitized input to the
Linux computer.
Real time Linux can be used in this project without any
further modification.
REFERENCES
[1]
Body
Temperature,
Bets
Davis,
http://health.yahoo.com/infectiousdisease-symptoms/body
temperature/healthwise
[2] Md.
Mazlan
Abdul
Jabar,
http://www.geocities.com/nazlen_2000/web
[3] Applications for Pico Products, Pico Technology Limited, St.
Neots, Cambridgeshire, UK, “Electrocardiogram (ECG) project for
DrDaq,” 2005
[4] http://www.picotech.com/applications/ecg.html.
[5] http://focus.ti.com/docs/solution/folders/print/330.html
[6] http://www.vision.net.au/~apaterson/science/hypoxia.htm
[7] http://www.faqs.org/docs/Linux-HOWTO/RTLinuxHOWTO.html#s3
[8] http://focus.ti.com/docs/solution/folders/print/330.html
[9] E. Hill, M.D. Stoneham, “Practical Applications of Pulse
Oximetry”, World Federation of Societies of Anaesthesiologists,
Issue 11, Article 4, 2000.
[10] Biomedical Instrumentation and Measurements,Prentice-Hall.
Md. Mokarrom Hossain born in Dhaka,
Bangladesh on 31st dec, 1987.Gradutated on
November, 2008 in Electrical & Electronic
Engineering from Islamic University of
Technology, Dhaka, Bangladesh. The degree
named as Bachelor of Science in Electrical &
Electronic Engineering. After finishing his
graduation he joined as a lecturer in a private
university named IBAIS University, Dhaka.
During his period of teaching he engaged
himself in extensive research works and projects which lead him to
publish several journals in various renowned national and international
journals. As a matter of progress he joined Stamford University Bangladesh
where he got to know several other contemporary young researchers who were
also working in various projects. That helped him to boost up his research
relative activities a lot. Now with the help of his colleagues he is continuously
working to improve the existing technology related to the field of Biomedical
Engineering. E-mail: [email protected]
A.S.M.Mohsin was born in Comilla, Bangladesh
in 1987.He received his B.Sc. in Electrical and
Electronic Engineering from the Islamic University
of Technology, Bangladesh in November 2008. He
has been working as a Lecturer at the Department
of Electrical and Electronic Engineering of
Stamford University Bangladesh, since 2009.He is
a member of IACSIT. His conducted courses in the
undergraduate level are Optoelectronics, Power
System Protection, Electronics, and Microwave Engineering etc. His research
interests include Nanotechnology/Photonics, Renewable Energy, Bio-medical
Engineering, and Communication. He has around 13 (International 6, National
7) published journal & 2 international conference paper in distinguished
journals & conferences in the field of Renewable Energy,
Nanotechnology ,Biomedical Engineering& Image Processing. E-mail:
[email protected]
Md. Nasimul Islam Maruf was born in Dhaka,
Bangladesh in 1986. He completed his B.Sc. in
Electrical and Electronic Engineering from the
Islamic University of Technology, Bangladesh in
November 2008. He has been working as a Lecturer
at the Department of Electrical and Electronic
Engineering of Stamford University Bangladesh,
Bangladesh since June 2009. His conducted courses
in the undergraduate level are Power System I,
Power Plant Engineering, Digital Signal Processing,
Control Systems Lab, Power Electronics Lab etc. His research interests
include Renewable Energy, Bio-medical Engineering, FACTS and Control
Systems.E-mail: [email protected]
Md. Asaduzzaman Shoeb was born in Barisal,
Bangladesh. He was graduated in Electrical and
Electronic Engineering from Islamic University
of Technology (IUT), Dhaka in 2008. He is a
lecturer at EEE Department of Stamford
University Bangladesh. He has a very diverse
research interest including renewable energy,
biomedical engineering, data communication
and control system. He is a member of IACSIT.
E-mail: [email protected],
[email protected].
Ifat-Al-Baqee is a Lecturer at Department of
Electrical and Electronic Engineering of Stamford
University Bangladesh at Siddeswari, Dhaka,
Bangladesh. He teaches electromagnetism and
electronics. His research activities are related to
Image Processing and Biomedical Engineering.
Lecturer Baqee is graduated from Military Institute
of Science and Technology, Dhaka, Bangladesh. He
is a co-author of an international journal paper, “A
Proposed Design for the Development of Vital Sign (Electrocardiogram)
Patient Monitoring System”, International Journal of Engineering Science
and Technology (IJEST) ISSN: 0975–5472 (online version), Vol. 2, Issue No.
10, page 5813-5817, 2010.E-mail: [email protected]
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